This invention relates to an enthalpy wheel by which heat and moisture are exchanged between a supply air stream and an exhaust air stream, and more particularly, the invention relates to a new desiccant paper suitable for fabricating into an enthalpy wheel which will aid in regulating the temperature and humidity of ambient air.
Enthalpy wheels or heat exchange wheels are mounted across a supply air stream and an adjacent exhaust air stream. The wheels rotate and continuously remove heat and/or moisture from one stream and return heat and/or moisture to the adjacent stream. The wheels are usually fabricated to provide a multiplicity of parallel pores or openings such as a honeycomb structure through which the air passes. Often, the wheels are formed from paperboard having one side corrugated and one side flat. The wheels are formed by winding the paperboard into the wheel shape to provide air passageways parallel to the axis of the wheel. The paperboard is comprised of a matrix or media capable of absorbing moisture an&or thermal energy from one stream and upon further rotation of the wheel, releasing the moisture and/or thermal energy to the adjacent stream which is to be conditioned. For example, the wheel can be used to recover moisture and heat from exhaust air at relatively high temperature for transfer to incoming air which is relatively dry and cool. Also, the wheel can be used to dehumidify and cool a moist, hot incoming stream by extracting moisture and heat from such stream and transferring the same to an exhaust stream from an air conditioned building that is relatively cooler and drier.
To improve indoor air quality, there is a great need to increase levels of outdoor air ventilated into buildings. However, it is important to minimize the cost associated with the introduction of outside air. For example, in winter, introducing cold, dry outdoor air to a building increases the heating load and adds to the fuel requirement. In summer, introduction of warm, humid outdoor air adds greatly to the air conditioning costs. Thus, to minimize costs associated with introduction of fresh air, heat exchangers such as rotating wheels have been employed to recover or reject, as needed, a portion of the sensible heat from the indoor air stream through exchange with the outdoor air stream. Further, some of the heat exchangers provide for latent heat exchange by incorporating a desiccant into the heat exchange surface. Thus, in summer moisture in an outdoor air stream being introduced to a building is removed and transferred to drier indoor air stream exiting the building. Conversely, in winter, moisture from air being ventilated from the building is adsorbed by the desiccant and subsequently desorbed into the drier outside air being introduced to the building. Thus, such heat exchangers transfer both sensible and latent heat and are often referred to as a total energy exchanger or an enthalpy exchanger. However, while these devices are very desirable for proposes of conserving energy and reducing heating and cooling bills, they have not found widespread acceptance because of their relatively high cost of production. The use or acceptance of less expensive devices fabricated from inexpensive materials such as plastics or paper and the like has always been greatly hampered by the fear of fire and smoke because the heat exchange device is mounted in the air duct to the building.
Thus, there is a great need for a safe, inexpensive heat exchange device that can be fabricated from inexpensive materials without fear of fire or smoke problems and yet provides a high level of sensible as well as latent heat exchange.
Prior references recognize the need for safe heat exchange devices. U.S. Pat. No. 4,093,435 discloses a rotary regenerative total heat energy exchanger having an asbestos-free heat exchange media formed by spirally winding flat and corrugated webs of aluminum foil and/or fully bleached, 45 lb Kraft paper constituted by 84% fibers and 16% salts. The patent notes that single-faced corrugated paperboard is made using a conventional silicate-type glue between a flat ply and a corrugated ply and that each ply is a Kraft paper treated with a mixture of ammonium sulfide and diammonium phosphate. Further, the patent notes that these constituents are hydroscopic, improve latent heat transfer capabilities and impart a fire-retardant characteristic to the material. However, such constituents can result in biological growth because the paper is primarily wood pulp based. Further, the wood pulp based papers tend not to age well in continuous long term use.
U.S. Pat. No. 4,134,743 discloses the use of zeolites as a desiccant in a regeneratable heat exchange apparatus. The apparatus comprises a rotatable wheel fabricated from a paper support material comprising cellulose fibers, glass fibers, asbestos, synthetic plastic fibers and zeolite desiccant in the amount of 1 to 90 wt. %. However, these materials are relatively expensive.
Adsorbents and fibrous materials useful in a desiccant wheel are disclosed in U.S. Pat. Nos. 3,024,867; 4,012,206; 4,769,053; 3,266,973; 3,338,034 and 4,255,171.
In prior references, U.S. Pat. No. 4,729,853 describes flame-retarding sealing compounds used for sealing fractures in walls for fire prevention, optionally reinforced with metal grids, mineral or glass fibers, wood or cellulose fibers, carbon fibers and ceramide fibers.
U.S. Pat. No. 5,130,184 discloses a fire barrier coating which is applied as an air-setting paint, is used to form a coherent fire-barrier on or between susceptible wood or plastic substrates, or other substances. Consisting of a paint-like slurry of three separate but compatible and mutually synergistic co-bonding systems, viz. magnesium "oxychloride" cement, plus high alumina mono-calcium aluminate cement, plus colloidal silica dispersed in dimethyl formamide (DMF), and utilizing an aqueous solution of magnesium chloride as the common hydrating fluid for the two cements, the coating retains its structural integrity through prolonged exposure to flame temperatures of 2000.degree. F.
U.S. Pat. No. 5,230,955 discloses thermoplastically re-formable plastic sheets with flameproofing means, characterized by a core layer 1-10 mm thick comprised of polyether sulfone or a similar thermoplastic, which core material has a content of at least 0.5 wt. %, preferably at least 2 wt. %, of a flame-protective additive, such as boron trioxide; and said sheet or plate further characterized by outer layers firmly adhering to and covering the two faces of the core layer, at least 0.05 mm thick and comprised of a thermoplastic having a lower proportional content of the flame-protective additives than the core layer; are particularly useful for interior structures in passenger conveyances, such as airplanes.
U.S. Pat. No. 4,370,249 discloses a fire-resistant, cellulose insulation and method, the cellulose insulation including a predetermined quantity of talc to impart the desired degree of fire-resistant characteristics to the cellulose. Predetermined quantities of boron compounds can be added with the talc to improve the fire-suppressant characteristics of the insulation. The method includes directing ground cellulose from the primary grinding stage into a surge bin to accommodate metering the talc with the cellulose to thereby assure the appropriate distribution ratio of talc in the cellulose.
U.S. Pat. No. 5,126,076 discloses low-flammability structural elements, particularly boards, and to a process for constructing them. The low-flammability structural elements are constructed utilizing combustible plastics waste material. They contain in addition non-combustible inorganic additives and a flame-proofing agent mixture. The components are held together by at least one hardened adhesive. Because of this build-up, the structural elements display, despite the combustible components, low-flammability.
U.S. Pat. No. 5,250,350 discloses a coextruded film with both gas barrier and fire retardant properties as well as good physical properties made up by melt coextrusion to form a four or five layer film product useful in making laminates for protective clothing or tarps. The five layer film has a Saran resin barrier core layer and LDPE skin layers on each face with intervening EVA glue layers. The four layer film has a Saran resin barrier core layer and a CPE skin layer on one face and an EVA skin layer on the other with an EVA glue layer between the barrier core layer and the CPE skin layer. Each skin layer and each glue layer contains about 8 to about 30 wt. % of a polyhalogenated organic/antimony oxide fire retardant and a small amount of a slip agent.
U.S. Pat. No. 5,225,236 discloses a protective drape and methods for using the drape to protect or shield an object against the harmful effects of accidental exposure to optical radiation, electrical discharge, heat or an open flame. The present invention comprises a flexible solid sheet and a composite scrim and includes methods for predicting/determining the suitability of a chosen metallic component for use in the instant drape.
U.S. Pat. No. 5,300,138 discloses a desiccant composition having a moderate Langmuir Type 1 moisture adsorption isotherm with a separation factor of frown 0.05 to 0.13. The composition contains silica gel, a modified 13.times. molecular sieve (modified by replacing at least 20% of the sodium cations with other metallic cations, e.g., potassium cations), and desirably a hydrophobic adsorbent (desirably a hydrophobic molecular sieve). The composition may be used as the desiccant in a rotary regeneratable dehumidification wheel, thereby significantly enhancing dehumidification performance and simultaneously removing a significant proportion of the airborne pollutants typically contained in indoor and outdoor air.
U.S. Pat. No. 5,304,419 discloses an enclosure for providing both a moisture free and particle free environment. A portion of the inner surface of the enclosure, that comprises an electronic device sealed in a container, is coated with a pressure sensitive adhesive comprising 4-40 vol. % of a solid desiccant. The preferred adhesive is a silicone pressure sensitive adhesive and the preferred desiccant is zeolite.
Yet, in spite of these disclosures, there is still a great need for a safe, inexpensive total heat exchange device free of smoke or fire problems and yet providing a high level of sensible heat exchange.